Hello David, Roderick and Howard
Having slept on the ideas of yesterday, there is in fact a very simple general calculation method that will give David all the pitches [within reason of course] he might care to find
If we treat the Myford metric banjo as purely a means of introducing external gearing ratios and marry that with the ones available from the screwcutting gearbox, the formula becomes
Pitch in inches = R (outside) x R (box) x leadscrew pitch in inches, where R is the ratio in each case
Taking David's example of 60 tpi
P [1/60] = Ro x Rb x 1/8 Hence Ro x Rb is 8/60= 0.1333. Matching that with a gearbox ratio of 0.1667 [the value for 48 tpi] gives a nice simple result for Ro of 0.8
So, in this example, David needs to set up a 40 tooth driver meshing with a 50 tooth driven wheel,linked by driver(s) as necessary, select a gearbox setting of 48 tpi and the resulting pitch will be 60 tpi
So David it is up to you now. You have been silent thus far.
Send me a PM stating your email address if you would like a copy of the whole 32 values of gearbox ratio. I can't unfortunately post it this way, there is a compatability issue with my computer that I am unable to resolve
Regards Brian